Conventionally, an electronic apparatus performing processes based on a map data is known as an onboard apparatus (navigation system) that displays a map image on a display device, calculates a guidance route to a destination point, or gives information about roads near the traveling road (e.g., see Patent Document 1).
A known example of map data represents a road network based on connections between links, which are components of a road. This type of map data stores a link data relating to characteristics of a link such as a road length, a traffic regulation and the like on a link-by-link basis.
Another known technique of the related art hierarchically represents a road network according to levels of detail in order to represent differently scaled maps or effectively search for routes (e.g., see patent document 2). A high-level layer represents a road network by connecting high-level links, each of which is a collection of multiple links forming a road network belonging to a low-level layer. The high-level layer selectively represents a part of the road network belonging to the low-level layer, thereby representing a main road. The conventional map data hierarchically represents road networks and stores road data (including link data) on a level-by-level basis.    Patent Document 1: JP-2000-283777A    Patent Document 2: JP-2005-70482A corresponding to US 2005/0058155
However, the hierarchically-represented map data of the related art requires a complicated work when being edited. Specifically, since the map data has road data (such as link data) for respective layers, an addition of a new road or a change of an existing road requires the road data of multiple layers to be edited in order for the map data to reflect this information. For addressing this difficulty, the road data of the layers may be complied. However, simply compiling data hinders easy access to necessary information and causes an unfavorable effect on performance (including processing time) of processes such as route search and the like.